The intention was to have an API method that accepts feature data `{Object|Element|Document|string}`, so this would require a runtime check.  Note that the `Element|Document` path is not handled yet, and when it is added it will come before the Object case.  Having `goog.isObject` in there is fine by me - as this code needs to change anyway.  We'll want to have something like `parseFeaturesFromString` etc that we use internally.